The overall goal of the proposed project is to determine the impact of long-term marijuana use on the neurocognitive functioning of individuals living HIV/AIDS. Marijuana use is common among individuals living with HIV/AIDS in part due to its medical use for the management of HIV-related symptoms. However, a growing body of research in the general population suggests that marijuana use can alter normal brain functioning and lead to neurocognitive impairment. Individuals living with HIV/AIDS who use marijuana may experience additional burden of neurocognitive impairment due to their vulnerability to HIV-associated neurocognitive disorders, which affect approximately 50% of this population. Despite the increased use of marijuana in this population and the potential for adverse interactive effects on neurocognitive functioning very little is known about the nature and extent of long-term marijuana use on neurocognition in HIV, as methodological problems including use of cross-sectional designs, small sample sizes and lack of sufficient control for other substances of use (e.g. alcohol, tobacco and other illicit substances) have limited previous work. Therefore, this proposal seeks to determine whether long-term heavy marijuana use and HIV disease confers adverse effects on the neurocognitive functioning of individuals living with HIV/AIDS. The Multicenter AIDS Cohort Study (MACS) - an ongoing prospective study with data available for 2,202 HIV-seropositive and seronegative men has tracked cognitive performance and marijuana use for over 26 years and therefore provides an ideal dataset to address this question. The specific aims of this project are to conduct secondary data analysis of the MACS to: 1) determine the dynamic patterns of marijuana use and identify factors associated with these unique patterns and 2) investigate whether long-term heavy marijuana confers significant changes in neuropsychological performance in tasks of learning/memory, speed of information processing and executive functioning. Group based trajectory analysis and linear mixed effects modeling will be used. The research proposed in this application have profound clinical implications regarding the use of marijuana in individuals living with HIV/AIDS and can inform future neuroAIDS research in this relatively understudied topic. In addition, this F31 grant will provide the applicant with mentored training in: 1) etiology, nosology, and consequences of substance use and use disorders and their measurement, 2) the neurocognitive consequences of substance use and HIV, 3) analyzing longitudinal data and advanced statistical modelling, 4) development of professional and career skills, 5) responsible conduct of research. Upon completion of this F31 training fellowship the applicant will have acquired the necessary skill to place him in a well-poised position to apply and attain an Post-doctoral training fellowship that allow the applicant to expand his training and research skill related to substance abuse and HIV